1. Field of the Invention
The present invention relates to an ink jet recording apparatus that records by discharging ink from discharging means to a recording medium.
2. Related Background Art
A recording apparatus having the functions as a printer, a copying machine, a facsimile equipment, or the like or a recording apparatus used as an output equipment for a complex electronic equipment or a work station including a computer, a word processor, or the like, is structured to record images (including characters, symbols, and the like) on a recording medium (recording material) such as a paper sheet, a thin plastic plate in accordance with recording information. The recording apparatuses are classified into those of ink jet type, wire dot type, thermal type, and laser beam type, among some others, depending on the recording method adopted by each of them, respectively.
For a recording apparatus of serial type that records while scanning in the direction intersecting the feeding direction (sub-scanning direction) of a recording medium, recording is performed on a recording medium entirely after the recording medium is set at a specific recording position by combining the recording operation by recording means (discharge means) that travels along the recording medium, and the feeding operation that feeds the recording medium in the direction intersecting the traveling direction of the recording means.
On the other hand, a recording apparatus of line type that records only in the sub-scanning direction in which a recording medium is being carried, images are recorded on a recording medium entirely after the recording medium is set at a specific position by feeding it by a given amount (pitch feeding) while the recording is performed continuously for a one-line portion altogether.
Of the recording apparatuses described above, the recording apparatus of ink jet type (ink jet recording apparatus) records by discharging ink from recording means (recording head) to a recording medium, which makes it easier to produce recording means (discharging means) compactly, and to record highly precise images at high speeds on an ordinary paper sheet without any particular treatment given to it. Therefore, this type can-operate at lower running costs. Also, being of a non-impact type, the ink jet recording apparatus has a lesser amount of noises, while making it easier to record color images using ink of multiple colors, among some other advantages. Particularly, the line type apparatus, which uses recording means of the fully multiple type that has many discharge ports arranged in the width direction of a recording sheet, makes it possible to record at higher speeds.
Particularly, the recording means (recording head) of the ink jet type that discharges ink by the utilization of thermal energy can be manufactured easily with the a highly densified arrangement of liquid flow paths (discharge port arrangement) by forming electrothermal converting member, electrodes, liquid path walls, ceiling, and the like filmed on a substrate by means of etching, deposition, sputtering, and other semiconductor manufacturing processes. In this way, its manufacture can be implemented more compactly.
Also, for an ink jet recording method or apparatus that can obtain high quality images on a recording medium, there is adopted the one that discharges an image quality enhancement agent (processing liquid) that insolubilizes or coagulates coloring material in recording ink, in addition to discharging recording ink (ordinary ink). Also, there are many demands on the materials of recording media (recording materials). In recent years, developments have been made to meet these demands so that the recording apparatuses can use cloth, leather, nonwoven textile, or even metallic material as a recording medium, besides paper (including thin paper sheet, processed paper sheet) and thin resin plate (OHP or the like). As specific apparatuses usable therefor, there is the aforesaid printer, copying machine, facsimile equipment, or the like or the recording apparatus used as the output equipment for a complex electronic equipment or work station including computer, word processor, or the like. Also, there may be cited those apparatuses and equipment that can be used for industrial production.
For the ink jet recording apparatuses described above, however, it is impossible to obtain color images having good image fastness and quality when images are formed on the recording medium which is defined as the so-called ordinary paper sheet, because the water-proofing of images thus recorded is insufficient or because it is not compatible to produce images in high density without causing feathering and running between colors when color images should be obtained.
As a method for improving the waterproof capability of images, it has been made practicable to use the ink that contains waterproof coloring material in it in recent years. However, the waterproof capability thus provided is still insufficient. Also, theoretically, this method has a drawback in that such ink is not easily soluble to water once it has been dried, and for that matter, the nozzles of a recording head tend to be clogged, and that the structure of the apparatus tends to be made more complicated in order to avoid the occurrence of such clogging.
Also, conventionally, there have been disclosed many techniques to improve the fastness of recorded images. In the specification of Japanese Patent Laid-Open Application No. 53-24486, a technique is disclosed for laking colors for fixation by giving post treatment to the colored object in order to enhance the wet fastness thereof. In the specification of Japanese Patent Laid-Open Application No. 54-43733, a recording method is disclosed in which two or more components are used to increase film formation capability when these components are in contact with each other at room temperature or at the time of being heated by use of an ink jet recording method. By the adoption of this method, it becomes possible to obtain prints that form the film that strongly adheres to the recording medium when the components are in contact with each other on it.
Also, in the specification of Japanese Patent Laid-Open Application No. 55-150396, there is disclosed a method for providing a waterproof agent for dyes of ink to form lake after images are recorded by an ink jet recording that uses water color ink. In the specification of Japanese Patent Laid-Open Application No. 58-128862, an ink jet recording method is disclosed for recording by the application of recording ink and processing ink, which are overlaid after provisionally discriminating positions of images to be recorded. The method is such that images are drawn by use of processing ink prior to the application of recording ink or processing ink is overlaid on recording ink whereby to form images beforehand or recording ink is overlaid on processing ink whereby to have drawn images beforehand, and then, processing ink is again overlaid on them to complete the image formation.
However, there are no disclosures in these documents as to recovery means for maintaining discharge reliability, the structure of recording head, the structure of ink tank, and the recording mode to improve the quality of recorded images, or the like, which is all characteristic of an ink jet recording apparatus.
Here, on the other hand, there are fundamental problems characteristic of the ink jet recording method. In other words, firstly, since recording is made by discharging ink droplets from the recording head to a recording medium such as a paper sheet, an OHP film, fine ink droplets (mist) generated aside from the main ink droplets or ink droplets rebounding from those discharged onto the recording medium are depositied to adhere to the discharge port surface of the recording head. Such adhesion of ink is concentrated around each of discharge ports in a large quantity. Then, paper particles and other foreign substances may adhere to such concentrated ink mist, thus hindering regular discharges. Therefore, ink is discharged in the unexpected directions (twisting), ink discharge is disabled (non-discharge), or some other malfunction may take place.
Secondly, when the recording head is not in recording operation or discharge ports are not allowed to discharge for a long time, to be exact, ink in the corresponding nozzles is evaporated and dried. As a result, ink becomes overly viscous and fixed, and causes nozzles to be clogged, leading to the twisting, non-discharge, and other defective discharges. To eliminate such drawback as this, an ink jet recording method should be provided with recovery means.
As means for solving the first problem, that is, means for cleaning off and removing foreign substances such as unwanted ink, paper particles adhering to the discharge port surface, which are brought about by the ink mist or rebounded ink droplets from the recording medium, a mechanism is generally adopted that clears (wipes) the discharge port surface by use of a blade formed by rubber or some other elastic material.
Also, as means for solving the second problem, it is generally practiced to adopt a mechanism given below. In other words, the discharge port surface of the recording head is covered by a cap when recording is at rest, thus preventing ink in the nozzles from being evaporated and dried so as not to allow ink from becoming overly viscous and fixed. If ink in the nozzles has become overly viscous and fixed to have caused defective discharges or if foreign substances cannot be removed by use of the blade, discharge is recovered to the normal state by exhausting the overly viscous ink in the nozzles using a suction pump connected with the aforesaid cap.
Further, for the recording operation of an on-demand type ink jet recording method, a plurality of discharge ports, which are arranged for one recording head, are not necessarily used entirely at all times. There are nozzles which are not used for a period longer than a certain time (namely, unused discharge ports). Also, for a color recording apparatus that has a plurality of recording heads, there may be some cases where all the discharge ports (nozzles) are not used, such as those provided for a recording head, but no recording data are transferred to them (a head which is not currently engaged in recording).
When the carriage travels or comes to a stop while discharge port surface is not capped, ink tends to be evaporated and dried in the discharge ports or on the surface thereof unless ink discharge is performed within a certain period of time. Then, the capability of ink discharges is lowered or the quality of recorded images is degraded after all. In order to prevent this phenomenon from taking place, it is generally practiced for an ink jet recording apparatus to discharge ink in a specific location periodically irrespective of recording data, thus exhausting ink from the nozzles and refresh ink therein for the maintenance of the normal discharge condition at all the time. Such ink discharge operation as this is called pre-discharge.
The ink discharging by means of such pre-discharge is performed toward a pre-discharged ink receptacle arranged separately in the interior of the cap of the recovery unit so that ink does not fly from the recording head unit and stains a recording medium and interior of the recording apparatus. For the suction recovery process described above, if the suction of the recording ink and processing liquid is performed by a suction pump shared by them for use, the recording ink becomes insolubilized in the suction pump, thus inviting a problem that the suction pump may be damaged.
Also, even if the suction means are separately arranged for use of recording ink and for use of processing liquid as respective systems, the processing liquid is caused to adhere to the discharge port surface of ink discharge means or enter the interior thereof when the ink suction recovery is performed. As a result, coloring material in ink is coagulated eventually with the probability that there occurs non-discharge of ink, deviation of discharging directions, or air leakage at the time of capping occurs. Meanwhile, there are various demands on the materials of recording media (recording material). In recent years, thin paper sheet and processed paper sheet (such as a paper sheet with punched holes for filing use, a scored paper sheet, an arbitrarily configured paper sheet) are in demand for use, besides paper sheet, thin plastic plate (OHP or the like) and other usual recording media.
For the serial type ink jet recording apparatus, a structure is disclosed, in which the capping operation of the recording head (discharge means) is executed by the utilization of the carriage operation in the main scanning direction, in the specifications of U.S. Pat. No. 5,563,638, Japanese Patent Laid-Open Application No. 63-4000, and others, for example. Such structure as this makes it possible to cap the recording head without any complicated mechanism to move the cap upward and downward. Also, this structure comprises only two systems arranged for driving the feeding system of recording medium and the carriage, with an advantage, among some others, that the capping operation is easily executable in the midway of recording on one sheet of recording medium.
In other words, if a capping operation should be executed by use of the feeding system of recording medium, the recording medium should be carried by an operation other than the usual stepping feed when the recording head is to be capped in the midway of recording. Therefore, such operation becomes undesirable from the viewpoint of the accuracy to be kept for feeding the recording medium. Also, when a capping operation is required, it may be possible to operate the capping without carrying the recording medium unnecessarily by partly cutting off the power transmission of the driving system for feeding the recording medium. In this case, however, backlash takes place in the essential array of feed driving of the recording medium inevitably. It becomes also undesirable to partly interrupt the system driving from the viewpoint of the accuracy that should be kept for feeding the recording medium.
Meanwhile, if the recording data are such as high resolution color information, it may take a time considerably to transfer such data from the computer to the recording apparatus per scanning operation in the main scanning direction of the carriage having discharge means (recording head) mounted on it.
Therefore, all the recording heads should be protected by capping means even in the midway of recording, because it is necessary to prevent ink from being dried or becoming overly viscous in the vicinity of discharge ports of the ink jet recording head while such data being transferred. Therefore, if only two driving systems are arranged for feeding a recording medium and driving a carriage, it becomes effective to execute the capping operation by the utilization of the carriage operation in the main scanning direction as a method needed for protecting the recording head without producing any adverse effect on the feeding accuracy of the recording medium as described earlier.
Also, it is practiced to maintain the quality of recording images in good condition by connecting a suction recovery pump with capping means in addition to the capping operation that can be executed by means of the carriage operation in the scanning direction as described above so that the ink clogging of the recording is eliminated or the overly viscous ink is removed by operating the suction pump. A suction recovery mechanism of the kind is disclosed in the specification of Japanese Patent Laid-Open Application No. 1-125239 and Japanese Patent Laid-Open Application No. 6-8460, for example.
However, the structures of the prior art described above present the drawback that it is impossible to selectively recover only a certain head by suction for an ink jet recording apparatus where a plurality of discharge means (recording heads) are arranged for color recording or the like. In other words, the conventional structure, in which the capping operation is executed for the recording heads by means of the carriage operation in the main scanning direction, is arranged to cap a plurality of recording heads altogether at a time. If a suction pump connected with any one of the caps is driven, ink is sucked from all the recording heads including those heads for which no recovery process has been required as yet. There is a disadvantage that ink is consumed wastefully. Here, therefore, various methods have been proposed in order to solve the problems that may lead to such drawback and disadvantage.
Nevertheless, for the conventional ink jet recording apparatus provided with a plurality of discharge ports (recording heads), a plurality of protection caps are used in order to prevent ink from being dried or becoming overly viscous on the circumference of discharge ports of each discharge means (recording heads), as well as to prevent adhesion of dust particles to them. Here, a part of caps dually functions as the suction cap for use of the suction recovery, and if the number of suction means is smaller than the total number of discharge means, there are still some cases where drawback may take place as described below.
In other words, if suction recovery is given to a plurality of discharge means that use ink of different colors, there may be the case where each of the caps abuts upon discharge means to be used for colors different from those used when each of them is capped for protection. As a result, the remaining ink adhering to the cap used for different color is transferred to the discharge port surface of discharge means, and then, the ink of different color on the discharge port surface is pushed into the interior of the discharge port when the wiping (wipe and clean) operation is executed after the suction recovery. To remove such ink of different color, there is a need for performing idle discharges to a certain extent so that ink of mixed colors is exhausted to the outside of the discharge ports accordingly.
In this way, although there is an advantage that the total number of caps can be curtailed by allowing them to function dually as protection caps and suction ones, not only the excessive amount of ink is consumed, but also, a disadvantage is still present that the recovery time becomes longer due to such idle discharges needed for removing ink of mixed colors.